Patients commonly receive drugs to treat a wide variety of medical conditions. While certain drugs may be administered via peroral, topical, transmucosal, or inhalation routes, other drugs are administered via injection or infusion. These injections or infusions may include intradermal, subcutaneous, intramuscular, intravenous, and intraperitoneal methods. Typically, injections or infusions involve the use of a hollow cannula or needle through which the drug passes from a container to the patient.
With regard to the subcutaneous and intramuscular injection routes, considerable attention has been devoted to providing a reproducible motion relative to the insertion of the cannula or needle through the skin to position the needle at a proper distance into the body, and then to provide a reproducible rate of delivery through the cannula or needle into the patient. Very often, providing a reproducible rate of delivery involves providing a reproducible motion for the movement of a plunger along the inside of a syringe or cartridge. Various mechanisms have been designed for controlled release of stored energy to advance the needle into the patient, and then to advance the plunger relative to the bore of the syringe or cartridge. Springs, motors, chemical reactions, and phase-changing materials have all been considered to provide the motive force for advancement of the needle and/or the plunger. Reproducible motion is considered fundamental to predictable drug delivery.
To the extent that a controller is included in such a drug delivery device, the controller controls the source of stored energy to ensure that it is released in a reproducible fashion. This may involve ensuring that various springs or motors are actuated such that one motion follows another in a predetermined sequence, thereby ensuring safe and effective delivery of the drug via the cannula or needle into the patient.